Added 'url' parameter a few days ago with the 1.2.1 release. The parameter has a maximum length of 512, and will be offered to the user as a redirect option when the notification is opened, as well as provide the redirect disclosure button (>) in the notification list.

In version 1.2 of the API, you say that "A success will return the following format, as well as the HTTP status code 200", but when I do this for retrieve/token I get a zero status code with success. here is the results: